1. Field of the Invention
The present invention generally relates to a method for accessing shared memories and a multiprocessor system using the accessing method in a distributed processing system in which various operations are processed by using plural processors.
2. Description of the Related Art
Recently, the development of the CDMA (code division multiple access) communication system has rapidly progressed and a processor system, which can operate in high-volume traffic corresponding to the expansion of mobile phone services and the popularization of data communications of huge amount of audio and video data in a wireless network, has been required. The processor system is generally realized by a multiprocessor system (for example, refer to Patent Document 1).
FIG. 1 is a block diagram showing a conventional multiprocessor system having shared memory cards. In the multiprocessor system shown in FIG. 1, n processor cards 101a to 101n, shared memory cards 104 and 105, and bus control cards 106 and 107 are connected to a global bus 108 in a multi-connection structure.
In the shared memory cards 104 and 105 in a redundant configuration, the same information which is common to the processor cards 101a to 101n is stored. The bus control cards 106 and 107 have a function to adjust the global bus 108 which the processor cards 101a to 101n use to access the shared memory cards 104 and 105. The processor cards 101a to 101n renew a common resource in the shared memory cards 104 and 105 while executing requested processes.
[Patent Document 1] Japanese Laid-Open Patent Application No. 2001-166960
However, corresponding to the expansion of services in an IDC (Internet data center) and communication services in the 3G, a large amount of communication data must be processed at high speed. However, in a multiprocessor system which processes large amounts of data by a distributed processing system, the conventional technology has difficulty in expanding the services due to limitations in increasing the throughput.
In the conventional multiprocessor system which includes shared memory cards shown in FIG. 1, in which the processor cards 101a to 101n and the shared memory cards 104 and 105 are connected by the global bus 108 in the multi-connection structure, as one of methods to increase the throughput, there is a method to add a new processor card. However, when a processor card is newly added, signal quality is degraded due to the increase of the connecting workload on the global bus 108. Consequently, there is a limitation to increasing the number of processor cards.
As a different method, there is a method to increase the throughput of the global bus 108. However, there is a limitation to increasing the throughput of the global bus 108 due to a limitation of the protocol of the global bus 108.
In addition, since the plural processor cards 101a to 101n are connected to the global bus 108 in order to access the shared memory cards 104 and 105, when the global bus 108 is hung up by some problem of a processor card 101x, other processor cards cannot access the shared memory cards 104 and 105.
Consequently, in the conventional multiprocessor system which requires large throughput, there are surely limitations for the throughput. In addition, when one of the processor cards has some trouble, the trouble interferes with processes in the other processor cards.